The present invention relates to detergent compositions containing nonionic, anionic, zwitterionic, or ampholytic surface-active agents or mixtures thereof, a particular type of soil release polymer comprising ethylene terephthalate and polyethylene oxide terephthalate in particular ratios and proportions, and a component which dissociates in aqueous solution producing lithium, potassium, alkaline earth, zinc or quaternary ammonium cations. The detergent compositions herein clean and provide improved soil release benefits to synthetic fabrics, particularly polyester fabrics, when used in an aqueous laundering system. One embodiment of the present invention comprises detergent compositions which contain surface-active agent, the select soil release polymer and an amount of a detergency builder such that the aqueous laundering solution of the detergent composition contains at least 1 .times. 10.sup.-4 moles/liter of alkaline earth metal ions. In addition, the detergent compositions herein permit the use of the disclosed soil release polymers in surfactant systems containing a broad range of surface-active agents.
Much effort has been expended in designing various compositions capable of conferring soil release properties to fabrics woven from polyester fibers. These fabrics are mostly copolymers of ethylene glycol and terephthalic acid, and are sold under a number of trade names, for example, Dacron, Fortrel, Kodel and Blue C Polyester. The hydrophobic character of polyester fabrics makes their laundering, particularly as regards oily soils and oily stains, difficult, principally due to the inherently low wettability of the polyester fibers. Since the character of the fiber itself is hydrophobic, or oleophilic, once an oily soil or oily stain is deposited on the fabric, it becomes bound to the surface of the fiber. As a result, the oily soil or stain is difficult to remove in an aqueous laundering process.
When hydrophilic fabrics, such as cotton, are soiled by an oily stain or soil, it is well recognized that the oil is much more easily removed than in the case of hydrophobic polyester fabrics. This difference in oil removal characteristics is apparently caused by a greater affinity of cotton fabrics for water and surfactant. The differing hydrophilic/hydrophobic characteristics of cotton and polyester are due in part to the basic building blocks of the fibers themselves. That is, since polyester fibers are copolymers of terephthalic acid and ethylene glycol, they have less affinity for water because there are fewer free hydrophilic groups, e.g., hydroxyl or carboxyl groups, where hydrogen bonding can occur. With cotton, which is a cellulose material, the large number of hydrophilic groups provides compatability with, and affinity for, water.
In terms of detergency, the most important difference between hydrophobic fabrics and hydrophilic fabrics is the tendency for oily soils to form easily removable droplets when present on a hydrophilic fabric and in contact with water and surfactant. The mechanical action of washing and the action of synthetic detergents and builders normally used in the washing step of the laundering process removes such oily droplets from the fabric. This droplet formation is in contrast to the situation which exists with a polyester (hydrophobic) fiber. Water does not "wick" well through hydrophobic fabrics and the oily soil or stain tends to be retained throughout the fabric, both because of the inherent hydrophobic character of the fabric and the lack of affinity of oily soils for water.
Since polyester and polyester blend fabrics, such as polyester cotton blends, are susceptible to oily staining, and, once stained, are difficult to clean in an aqueous laundry bath, manufacturers of polyester fibers and fabrics have sought to increase the hydrophilic character of the polyester to provide ease of laundering.
A number of approaches to the problem of increasing the hydrophilic character of polyester fabrics and fabric blends have been taken. Many of these approaches involve a process employed by the textile fiber manufacturer or the textile manufacturer. For example, U.S. Pat. No. 3,712,873, Zenk, issued Jan. 23, 1973, discloses the use of polyester polymers in combination with quaternary ammonium salts as fabric treating compositions. Terpolymers having a molecular weight in the range from 1,000 to 100,000 and a molar ratio of terephthalic acid:polygolycol:glycol from 4.5:3.5:1 are disclosed. These compositions may be applied by spraying or padding onto textiles containing polyester or polyamide synthetic textile materials for the purpose of improving the soil release characteristics of these materials.
U.S. Pat. No. 3,959,230, to Hays, issued May 25, 1976, teaches that the soil release properties of polyester-containing fabrics may be improved by treating those fabrics with dilute aqueous solutions of ethylene terephthalate/polyethylene oxide terephthalate copolymers having a molar ratio of ethylene terephthalate to polyethylene oxide terephthalate of from about 25:75 to about 35:65, the polyethylene oxide having a molecular weight of from about 300 to 700 and the molecular weight of the entire polymer being in the range of from about 25,000 to about 55,000. U.S. Pat. No. 3,479,212, Robertson et al., issued Nov. 18, 1969, and U.S. Pat. No. 3,416,952, McIntyre et al., issued Dec. 17, 1968, disclose the use of ethylene terephthalate/polyethylene oxide terephthalate copolymers in the manufacture of polyester articles to provide them with enhanced hydrophilic character, and hence enhanced oily soil removal effect.
It has also been suggested that soil release polymers may be incorporated into detergent compositions so that when polyester-containing fabrics are washed in liquors containing these detergent compositions, the fabrics are modified so that oil-containing stains subsequently formed on the fabric are more easily removed on subsequent washing. Even if the fabrics are treated by the manufacturer, the treatment benefit is diminished as the fabrics age, mainly due to removal of the soil release polymer through washing in ordinary detergent products. Thus, the use of detergent compositions containing soil release polymers provide fabrics washed in them with an ongoing soil release benefit.
British patent specification No. 1,377,092, Bevan et al., published Dec. 11, 1974, teaches the use of polyoxyethylene glycol/polyethylene terephthalate copolymers as soil-release agents in detergent compositions containing nonionic surfactants. It is indicated that the presence of anionic surfactants in the detergent compositions should be avoided, since such surfactants would decrease the soil-release properties of the compositions. Builders may be included in the compositions disclosed in the British Patent. There is, however, no indication that the presence of specific builders or cations will have any effect on the soil-release performance of the copolymer-containing detergent compositions.
South African Patent Specification No. 72/7174, Bevan, discloses a process by which a terephthalate copolymer of cellulose ether soil-release agent is dispersed in a granule for use in a granular laundry detergent composition.
U.S. Pat. No. 3,962,152, to Nicol et al., issued June 8, 1976, teaches the use of specific ethylene terephthalate/ethylene oxide terephthalate copolymers in solid dry detergent compositions.
Although the use of terephthalate/ethylene oxide terephthalate copolymers as soil-release agents in detergent compositions has been disclosed in the art, there has been no recognition of the fact that the presence of free cations in the aqueous laundry solution of the detergent compositions, has any effect on the deposition and soil-release performance of the polymer-containing compositions. It has now been found that by controlling the presence of free cations in the aqueous laundry solutions of detergent compositions containing terephthalate copolymer soil-release agents, these detergent compositions will provide increased deposition of the polymer on the fabric and superior cleansing of oily soils and stains. For example, if the detergent compositions are formulated such that the aqueous laundry solution contains at least 1 .times. 10.sup.-4 moles/liter of free alkaline earth metal hardness ions, improved cleaning of oily soils will result. In contrast, detergent compositions are generally formulated so as to eliminate all free hardness ions in the wash solution.
It is, thus, a primary object of this invention to provide detergent compositions which exhibit excellent cleaning performance while concurrently imparting soil-release properties to hydrophobic fabrics treated therewith.
It is another object of this invention to provide detergent compositions comprising nonionic, anionic, zwitterionic, and ampholytic surfactants in combination with polymeric soil-release ingredients.
It is a further object of this invention to provide detergent compositions comprising soil-release polymers having specific molar ratios of ethylene terephthalate to polyethylene oxide terephthalate.
It is a further object of this invention to provide a method for the improved removal of oily soils from hydrophobic fibers.
The above and other objects are accomplished by formulating detergent compositions containing water-soluble surfactants and polymers composed of terephthalate esters, as described hereinafter.